Optimizing heat transfer during the charge and discharge of thermal stores is crucial for high performance of solar thermal systems for domestic and commercial applications. This study models a sensible water storage tank for which discharge is accomplished using a heat exchanger immersed in the storage fluid. The heat exchanger is a two-dimensional isothermal cylinder in an adiabatic enclosure with no initial stratification. An adiabatic shroud and baffle whose geometry is parametrically varied is placed around and below the cylinder. Transient numerical simulations of the discharge process are obtained for 105 < RaD < 107, and estimates of the time needed to discharge a given fraction of the initial stored energy are obtained. We find that a short baffle is least effective in increasing heat transfer rates. The performance benefit is greatest early in the transient discharge period when the buoyant flow in the store is strongest. As with all flow control devices, the benefit decreases as energy is extracted from the tank and the temperature difference driving the flow decreases. The use of a shroud increases the transient Nusselt number by as much as twentyfold.
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e-mail: sandra.boetcher@erau.edu
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February 2012
Research Papers
Use of a Shroud and Baffle to Improve Natural Convection to Immersed Heat Exchangers
Sandra K. S. Boetcher,
Sandra K. S. Boetcher
Mem. ASME
Department of Mechanical Engineering,
e-mail: sandra.boetcher@erau.edu
Embry-Riddle Aeronautical University
, Daytona Beach, FL 32114
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F. A. Kulacki,
F. A. Kulacki
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455
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Jane H. Davidson
Jane H. Davidson
Fellow ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455
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Sandra K. S. Boetcher
Mem. ASME
Department of Mechanical Engineering,
Embry-Riddle Aeronautical University
, Daytona Beach, FL 32114e-mail: sandra.boetcher@erau.edu
F. A. Kulacki
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455
Jane H. Davidson
Fellow ASME
Department of Mechanical Engineering,
University of Minnesota
, Minneapolis, MN 55455J. Sol. Energy Eng. Feb 2012, 134(1): 011010 (7 pages)
Published Online: November 29, 2011
Article history
Received:
January 24, 2011
Revised:
August 26, 2011
Online:
November 29, 2011
Published:
November 29, 2011
Citation
Boetcher, S. K. S., Kulacki, F. A., and Davidson, J. H. (November 29, 2011). "Use of a Shroud and Baffle to Improve Natural Convection to Immersed Heat Exchangers." ASME. J. Sol. Energy Eng. February 2012; 134(1): 011010. https://doi.org/10.1115/1.4005089
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